Hepatic steatosis, also known as fatty liver disease, is a condition where hepatocytes suffer from abnormal intracellular accumulation of fat, mostly in the form of triglycerides (TG). The two main types of hepatic steatosis are alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD). NAFLD is the most common cause of chronic liver disease in the United States. Hepatic steatosis can lead to progressive hepatic disease and is a risk factor for cardiovascular disease and diabetes. Liver biopsy with histologic analysis is commonly used for diagnosing and grading a fatty liver. However, due to the invasive nature of liver biopsy with histologic analysis and limitations such as lack of representation of the entire liver, non-invasive assessments based on cross-sectional imaging are being investigated.
Ultrasound imaging has been used for evaluating hepatic steatosis. Ultrasound imaging uses sound waves with frequencies higher than those audible to humans (>20,000 Hz). These sound waves are pulsed into tissue using a probe. The sound waves echo off the tissue. Different tissues reflect different degrees of sound. These echoes are analyzed through signal processing and are further processed using clinical ultrasound reconstruction algorithms to reconstruct ultrasound images for presentation and interpretation by an operator. Many different types of images can be reconstructed using ultrasound imaging. One such type is a B-mode image which displays the acoustic impedance of a two-dimensional cross-section of tissue. Ultrasound imaging, however, suffers from poor repeatability and reproducibility in evaluating hepatic steatosis.
Unenhanced computed tomography (CT) has been used for evaluating hepatic steatosis. Using unenhanced CT, fatty liver can be diagnosed based on its attenuation value and relative relationship with the spleen and blood. However, the sensitivity of unenhanced CT is limited.
Magnetic resonance imaging (MRI) is currently the most accurate and precise non-invasive imaging modality for diagnosing and quantifying hepatic steatosis. MRI data can be processed to estimate proton density fat fraction (PDFF) as a measure of fractional fat content. However, MRI is expensive.
Although techniques for detecting and grading hepatic steatosis have been considered, improvements are desired. It is therefore an object to provide a novel method and system for estimating fractional fat content of an object using thermoacoustic imaging.